It is one of two failed dishes that result from using incompatible ingredients along with Dubious Food. In early beta builds and demos of Breath of the Wild there was a third failed dish called Failed Experiment.

Cooking animation

When cooking this food, the puff animation is not the usual one but a not-so appealing one, made out of smoke and sound of breaking glass indicating failure. As its name implies, Link has visibly hard time chewing Rock-Hard Food when he consumes it, though it will not hurt him but restores a few heart containers.

Moza

Near the Ishto Soh Shrine, Link encounters Moza a female Hylian chef who apparently specializes in making failed dishes. She will teach Link recipes to improve health restoring effect of failed dishes by using certain incompatible ingredients. She has even named her recipes despite explicitly resulting in either Dubious or Rock-Hard Food.

She has a single recipe for Rock-Hard Food which she calls "Lavish meat dish". It is prepared by cooking either Raw Meat or Raw Bird Drumstick with any Ore Deposits' materials, save for Rock Salt granting "Salted" meat dishes. Unlike the others, this recipe will not increase the amount of hearts restored.